1. Field of the Invention
The present invention is related to a microscope system, and particularly to a microscope system that performs structured illumination.
2. Description of the Related Art
In recent years, a technique of obtaining images of a specimen at a resolution exceeding the resolution limit of imaging optical systems including an objective lens (this resolution is referred to as a super-resolution hereinafter) has been developed and put into practical use. As an example of a super-resolution technique, a microscopy referred to as structured illumination microscopy (SIM) is known. According to Kohler illumination, which is a widely accepted illumination method, specimens are illuminated as evenly as possible, whereas structured illumination microscopy illuminates specimens in such a manner that interference with illumination light forms a fringe illumination pattern on the specimens. Thereby, light including specimen information with frequencies higher than those used in other techniques can contribute to image formation so that a specimen image at a resolution exceeding the resolution limit of imaging optical systems (referred to as a super-resolution image, hereinafter) can be generated. Note that according to structured illumination microscopy, the performance based on resolution can be doubled at most under normal circumstances.
A device using structured illumination microscopy as described above is disclosed by, for example, Japanese Laid-open Patent Publication No. 2006-268004. This document discloses a microscope device that forms interference fringes on a specimen by causing interference of positive or negative 1st-order diffracted light from the grating. A microscope device that utilizes 0th-order diffracted light in addition to positive or negative 1st-order diffracted light for causing interference in order to attain sectioning effects is also known.
According to structured illumination microscopy, super-resolution images are generated by performing numerical operations using a plurality of images obtained with different phases of interference fringes that constitute the illumination pattern. This makes it necessary to pick up images of a specimen a plurality of times with different phases of interference fringes. A microscope device disclosed by Japanese Laid-open Patent Publication No. 2006-268004 is capable of picking up images of a specimen with different phases of interference fringes by changing the angle of a steering mirror set close to a pupil conjugate plane of an objective lens.
Also, super-resolution images generated by structured illumination microscopy have super-resolution characteristics only in the directions of interference fringes formed on a specimen. Accordingly, it is usually desirable to pick up images of a specimen a plurality of times with interference fringes in various directions in order to suppress the direction dependency of super-resolution images. Regarding this point, Japanese Laid-open Patent Publication No. 2006-268004 discloses a microscope device that can form interference fringes in three different directions by using a grating having a periodic structure in three directions that are different from each other by sixty degrees.
According to structured illumination microscopy, intervals between interference fringes to be formed on a specimen and movement amounts of interference fringes from one image pick-up operation to another vary depending upon the magnification and the numerical aperture of an objective lens, and upon the wavelength of illumination light. Accordingly, when a different objective lens is used, it is desirable to form on a specimen an illumination pattern appropriate to optical parameters (such as the magnification or numerical aperture) of that objective lens, and when a different light source is used, it is also desirable to form on a specimen an illumination pattern appropriate to optical parameters (such as the wavelength of illumination light) of that light source.